Need Van's instruments/ Alternator advice

[Cloudboy]

Something burned up several of my Van's engine instruments; CHT, EGT, fuel quantity, fuel pressure, oil temp and pressure. I saw Stein at Oshkosh and he said he had several he had removed for panel upgrades. He generously gave me some of the ones I need. I still need CHT and EGT as well as the low pressure fuel gauge. If anyone has some laying around gathering dust, I am interested in them.
Also, is there anything other than a malfunctioning voltage regulator and/or alternator that could have caused the damage? I hate to just replace parts looking for a problem. I have a Japanese, internally regulated alternator that is putting out 14.2 volts. I don't think a test at the auto parts store will show a problem. Is there a way to test the regulator or a simple way to add overvoltage protection?
Feel free to call me: Steve 509-991-8915

[Untainted123]

My understanding is that all of the old "analog" gauges are simply measuring resistance across a resistor (the sensor) and correlating that to a scale with a needle (the gauge), essentially like the old voltmeters before they all became LCD displays with numbers.

So, I would imagine all of them could be ruined by over voltage or perhaps over amperage, effectively ruining the resistor (the sensor), perhaps making the gauge have to swing way past it's normal stops and ruining it. It's a theory anyway.

Most of the sensor have published resistance values for a given temperature or pressure, and can be easily checked with a voltmeter (proving which is bad, the sensor or the gauge).

Some of the old Van's gauges actually had a troubleshooting procedure for them also, read this thread for a discussion of it.

[Cloudboy]

Thanks untainted. You are correct, many gauges are milliamp meters and the current through them varies with the resistance of the sensor. I think the problem must have been over voltage. So far, all the sensors have been fine but on autopsy, the meters themselves have melted and/or have discolored components. I was hoping some builders saved their old gauges when they went to glass panels.
When I last flew, I had a strong burning smell in the cockpit giving me a sore throat, etc. I suspected overvoltage so I kept the alternator on and watched the volt meter. I had a solid 14.2 volts; just what I expected. I assumed that a failed voltage regulator would show overvoltage on the voltmeter. I don't understand the failure modes of regulators and maybe it was just a quick spike. One melted gauge was bad enough that I seems like more than a quick spike. The plastic case was substantially deformed, some capacitors destroyed and small components melted off the circuit board. The failed gauges were wired in parallel, not series, so I don't think over current would have wiped out several at once.
I would sure like to hear anyone's ideas about voltage regulator failure modes and, especially about surplus instruments.

[BoydBirchler]

An overvoltage is pretty simple to add. I believe you can obtain the necessary components from B&C. It consists of a diode that has an approximate switch on value of 15 volts, that is used to crowbar (short out) the 2 amp field breaker.

[Cloudboy]

Good advice Boyd. I ordered a B&C alternator and regulator yesterday. I'm still looking for instruments.

[Mikeyb]

Since it’s The engine mounted instruments and they saw a massive overcurrent one might suspect the Engine/airframe ground degraded and caused the starter/alternator current to return through the engine instruments.

[Cloudboy]

Good thought Mikey. I checked the engine ground and it was firmly connected. But I think I better make sure the connections are clean.
Both fuel quantity gauges were fried as well and I don't think they connect to the engine. Also, my ICOM radio quit working. I took the case off and found a burned spot where a device labeled F1 was mounted on a circuit board. A friend found the repair manual on line and found the part number for the fuse. We replaced it and the radio is working fine.
Some of my failed gauges have a burned resistor but the colored bands are discolored from the heat and we cannot read the values. If I had a schematic for the gauges with parts specifications, I think I could fix them.
As it is, I still need the CHT and EGT gauges as well as the low pressure fuel pressure gauge. I'm still hoping someone has them sitting in a box somewhere.

[FinnFlyer]

Originally Posted by BoydBirchler

An overvoltage is pretty simple to add. I believe you can obtain the necessary components from B&C. It consists of a diode that has an approximate switch on value of 15 volts, that is used to crowbar (short out) the 2 amp field breaker.

Note that this requires an alternator with external regulator.

Having said that, I'm actually using a Mazda RX-7 alternator and its internal regulator where I was able to disconnect internal supply to the internal regulator and supply it from circuit breaker with over voltage crowbar. Depends on alternator design if that is feasible.

Finn

[FireMedic_2009]

You can add another contactor to run the the B-lead through it from the alternator and use the over voltage protection module to trip the contactor. You need to understand what you are doing and how to connect it.

[JohnTod]

I have an EGT and CHT with senders I no longer need. They are the Same as Vans units but with no Vans label. Free to you for shipping. Call me at 858 945 0079.